The Villar Perosa submachine gun is one of the most unusual weapons that emerged during the WW1. The name of the weapon comes from the name of the company that manufactured these guns, the Officine Villar Perosa (OVP in short). This gun was originally designed in 1914 by famous Italian small arms designer Bethel Abiel Revelli as an aircraft weapon. In this role it found no success, as it was designed to fire low-powered 9mm Glisenti ammunition, which was even weaker than dimensionally similar 9x19 Luger ammunition. In 1915 the Villar-Perosa was converted for ground applications, with introduction of variety of mountings, including light tripods or carrying trays (which were carried on shoulder straps or put on the ground for more stable position and less exposure to enemy fire). Later on, a wooden rifle-type stock was designed for Villar-Perosa, so it could be fired more or less comfortable from the shoulder, thus creating the first practical submachine gun in the world. After the war, some of the original Villar-Perosa weapons (which were actually assemblies of two similar guns) were disassembled into halves, and put into rifle type stocks, with addition of the rifle-type triggers. Such conversions were known as Villar Perosa OVP M1918 (when done by Villar Perosa). A slightly improved version of the same design was also produced by Beretta company, and it was known as Beretta M1918.

The Villar Perosa M1915 weapon was assembled from two guns of exactly same design and appearance, which were held together by the plate at the front of the receiver and by the twin spade grips assembly at the rear. Each gun has its own trigger, operated by a separate thumb button between spade grips. The guns themselves used delayed blowback action, in which the delay of the initial opening of the bolt was achieved by rotation of the bolt through the bolt handle that slid against the inclined part of the cocking handle slot. The bolt rotation, combined with separate firing pin, provided safety measure against premature ignition of the cartridge, as the firing pin was able to go forward and strike the primer only when bolt was in battery and completely rotated. Guns fired from open bolt, in full automatic mode only. Due to the lightweight bolt and powerful springs, the rate of fire was excessively high for the ground applications, being between 1200 and 1500 rounds per one gun (rising up to 3000 rounds per minute when both guns were fired at once). The feed was from detachable box magazines, holding just 25 rounds each, so one magazine was forth just one second of the continuous fire. Magazines were inserted into the each gun vertically from the top, ejection was to the bottom. Sights were located between the guns, with rear sight being built into the spade grip assembly and the front sight into the front plate that held both guns together.The OVP M1918 submachine gun was made from one gun from the original M1914 twin weapon, with added shoulder stock and a new dual trigger setup, which allowed for single shots (rear trigger) and full automatic fire (front trigger). The cocking of the bolt was achieved by pulling back the knurled sliding sleeve, located around the receiver. Feed arrangement was similar to the original twin weapon, with top-mounted box magazine. The rate of fire was somewhat lower, making this gun somewhat more controllable and more useful in ground combat. A new set of sights was installed, with line of sight necessarily moved to the left to clear the magazine.